Shock-resistant microphone



April 22, 1969 H. J. ecu.

SHOCK-RES ISTANT MICROPHONE Filed Nov. 26, 1965 FIG.

F/GZ

FIG. 3

INVENTOR H. J. BOLL United States Patent 3,440,363 SHOCK-RESISTANT MICROPHONE Harry J. Boll, Berkeley Heights, N.J., assignor to Bell Telephone Laboratories, Incorporated, New York, N.Y., a corporation of New York Filed Nov. 26, 1965, Ser. No. 509,887 Int. Cl. H04r 19/04 U.S. Cl. 179-121 8 Claims This invention relates to an electroacoustic transducer and particularly to a shock-resistant microphone.

The advantages of solid state devices of various types as electromechanical transducers, particularly in microphones, have been recognized almost from the inception of the transistor. Exemplifying such arrangements are the disclosures of Patent 2,497,770 to R. L. Hanson, Patent 2,632,062 to H. C. Montgomery and Patent 2,929,885 to C. W. Mueller. Various forms of PN junction devices have been found to exhibit highly desirable response characteristics, particularly from the standpoint of sensitivity and the ability to retain these characteristics with time and usage. However, efforts to couple solid state transducers of the type described to acoustic-to-mechanical transducers, typically a diaphragm, have met with difliculties. In particular, the relative fragility of the various solid state transducers has made them extremely subject to mechanical damage when adapted to uses which entail rough handling, such as for transmitters in tele phone handsets. Moreover, other types of stress-sensitive, solid state transducers, including piezoelectric and magneto-strictive types, likewise are subject to this difliculty. Therefore, an object of this invention is a shock-resistant electroacoustic transducer.

A more particular object is a stress limiting coupling between the acoustic-to-mechanical transducer and the mechanical-to-electrical transducer.

In a broad aspect the invention is directed to electroacoustic transducers comprising an acoustic-to-mechanical transducer such as a diaphragm for changing sound energy to mechanical energy, a stress-sensitive electromechanical transducer for changing mechanical energy to electrical energy, and mechanical coupling means for transmitting force between these two transducers. In particular, the intermediate force transmitting means provides that only forces below the level which would damage the electromechanical transducer are transmitted.

The invention is advantageously used with any stresssensitive transducer and particularly those of inherently fragile structure and susceptible to damage from shockinduced stresses. Exemplary of such transducers are the types disclosed in Patents 3,137,834; 3,186,217, and application Ser. No. 80,672, filed Jan. 4, 1961, now Patent No. 3,270,554 all of W. G. Pfann and application Ser. No. 282,792, now Patent No. 3,312,790 filed May 23, 1963 of M. E. Sikorski; all of these disclosures being assigned to the assignee of this application.

Reference is made here to the application, Ser. No. 509,886 of H. J. Boll and W. S. Boyle made on the same date as this application and assigned to the same assignee. The reference application discloses and claims another arrangement of a shock-resistant electroacoustic transducer.

An embodiment of an electroacoustic device in accordance with this invention comprises a mechanical linkage utilizing a double-fulcrumed bar upon which the stress responsive element is mounted. The driving member of an acoustic diaphragm is connected to the free end of the double-fulcrumed bar which has one pivot point at the other end and a second pivot point near its middle. A spring force is provided urging the bar against the fulcrum pivot points. The stress responsive element is incorporated in the bar member near its middle where it is subject to the maximum bending moments applied from the diaphragm. Accordingly, deflection of the diaphragm resulting from the impact of sound energy produces bending of the bar member and induces an electrical response within the transducer element. Forces of excessive magnitude, however, such as those resulting from dropping the device, are dissipated without damaging the transducer as a consequence of excessive distortion of the bar member. This occurs because the bar member lifts off one or the other fulcrum, depending on the direction of the deflecting force. However, after the impact of such an excessive force the device resumes its previous condition, and there is no lengthy interruption in operation.

Accordingly, features of the device in accordance with this invention are its relative simplicity and ease of fabrication and adjustment.

The invention and its other objects and features will be more clearly understood from the following detailed description taken in connection with the drawing in which each of FIGS. 1, 2 and 3 show in schematic form the basic portion of the shock-resistant arrangement in accordance with this invention.

FIG. 1 shows the normal or low stress condition of the apparatus during normal operation. FIGS. 2 and 3, on the other hand, illustrate the condition of the device when the driving force and consequent deflection exceeds the normal limits, first in one direction and then in the other.

The arrangement shown in FIG. 1 shows simply the basic operating elements of the shock-resistant electroacoustic transducer in a form of illustration which corresponds to FIG. 2 of the above-referenced application. Accordingly, it will be understood that the device of FIG. 1 may be incorporated in, for example, a telephone handset as illustrated likewise in the reference application.

The arrangement of FIG. 1 shows a portion of a header 11 and a mounting disc 12. A metal strip 14 is secured on the mounting disc and is linked by means of the leaf spring member 15 to the bar member 16. In particular, as may be seen clearly by referring to FIGS. 2 and 3, the spring member 15 is secured at the one end to the metal strip 14 and at the other end to the bar member 16. This leaf spring member 15 thus constrains the bar member 16 and metal strip member 14 to stay in substantial alignment. The ends of the metal strip member 14 substantially constitute the fulcrums or pivot points about which the bar member 16 may rock. The bar member 16 is biased against these pivot points by the spring member 13 which is secured to the mounting disc 12.

The free end of the bar member 16, is attached by way of the connecting rod 20 to the dome member 21 which is an integral part of diaphragm 22 at its center. Near the midpoint of the bar member 16, and particularly near a portion where the bending force is at its maximum, is an electro-mechanical transducer 17. This transducer 17 has a pair of electrode connections 18 and 19 for transmitting the electrical signal therefrom in response to applied stress.

Thus, movement of the connecting rod 20 in response to diaphragm movement deflects the end of the bar member 16 and, for forces within the normal operating range, produces a bending of the bar member and a stressing of the transducer element 17, thus generating or modulating an electrical signal. However, if as shown in FIG. 2, an excessive force is applied which throws the diaphragm 22 downward with a force sufliciently great to damage or destroy the transducer 17 were the bar member 16 fixed at its inner end, then such damage is avoided by lifting the beam off one pivot as shown. correspondingly, if

the excessive force on the diaphragm is upward, the bar member 16 rocks on its inner pivot point, and again avoids the application of excessive stress to the transducer 17. Thus in effect the bar member 16 has an unsupported end subject to deflection by the applied force and a supported end which is fixedly supported until the applied force exceeds a certain value when it becomes resiliently supported. The bar member 16 then is the vehicle for the application of stress to the electromechanical transducer element 17.

It is evident that during each excessive deflection as shown in FIGS. 2 and 3, the electrical response is distorted. However, these intervals are momentary and immediately upon resumption of normal deflections the device resumes its condition as shown in FIG. 1 and normal electrical response is resumed.

The device described above may be produced in a variety of forms and in exceedingly minute dimensions. In particular, the techniques of microelectronics may be used to fabricate the members 14, and 16 and the transducer element 17. In one embodiment the bar member 16 may be of silicon and the transducer element 17 may comprise a diffused resistor within the silicon bar. The leaf spring 15, bonded at one end to the bar member 16 and at the other end to the metal strip 14, may be produced by masked metal evaporation and selective etching steps of the type disclosed in the application of M. P. Lepselter, Ser. No. 388,039, filed Aug. 7, 1964 and assigned to the same assignee as this application.

The constraint furnished by the spring member 13 balanced against the dimensions of the bar 16 and magnitude of the diaphragm driving forces, in general determine the force cutoff level above which the device is disabled. In particular, the device may be adjusted so that the bar member 16 lifts off one or the other pivot or hinge point at a value of applied force just below that which would otherwise result in overstressing and damage to the transducer 17.

In another arrangement in accordance with the invention, the stress-sensitive transducer element 17 may be separated from the bar member 16. For example, the transducer element 17 may be mounted on a fixed base and force applied to it by means of a stylus attached to the bar member 16 at either fulcrum point. Thus, in effect, in this arrangement the stress-sensitive transducer supports one of the fulcrums which in turn supports the bar member.

Although the invention has been disclosed in terms of a particular embodiment, it will be understood that the principle involved may be utilized in a variety of arrangements which may be devised by those skilled in the art and which likewise will fall within the scope and spirit of the invention.

What is claimed is:

1. A shock-resistant electroacoustic transducer comprising, a first means for translating sound energy to mechanical energy, second means for trnaslating mechanical energy to electrical energy, third means for transmitting force from said first to said second means including a bar member having an unsupported first end and a supported second end, further including coupling means conmeeting said first means to said first end for transmitting force therebetween, and support means for said second end which is fixed when the force transmitted is just below that which would damage said second means, and which is resilient when the force is greater.

2. Apparatus in accordance with claim 1 in which said support means comprises a pair of fulcrums and a biasing member opposed thereto.

3. Apparatus in accordance with claim 1 in which said first means comprises a diaphragm.

4. Apparatus in accordance with claim 1 in which said second means comprises a stress-sensitive transducer.

5. Apparatus in accordance with claim 4 in which said stress-sensitive transducer is integrally attached to said bar member.

6. Apparatus in accordance with claim 5 in which one of said fulcrums is at said second end of said bar member and the other fulcrum is near the mid-portion of the bar member, and said stress-sensitive transducer is attached to said bar member near said other fulcrum.

7. Apparatus in accordance with claim 2 in which one of said fulcrums is supported by said second means.

8. Apparatus in accordance with claim 7 in which said second means comprises a stress-sensitive transducer.

References Cited UNITED STATES PATENTS 3,377,440 4/ 1968 Roberton. 3,383,475 5/ 1968 Wiggins. 3,404,243 10/ 1968 Krieger.

KATHLEEN H. CLAFFY, Primary Examiner.

ARTHUR A. MCGILL, Assistant Examiner.

US. Cl. X.R. 317235 

1. A SHOCK-RESISTANT ELECTROACOUSTIC TRANSUCER COMPRISING, A FIRST MEANS FOR TRANSLATING SOUND ENERGY TO MECHANICAL ENERGY, SECOND MEANS FOR TRANSLATING MECHANICAL ENERGY TO ELECTRICAL ENERGY, THIRD MEANS FOR TRANSMITTING FORCE FROM SAID FIRST TO SECOND MEANS INCLUDING A BAR MEMBER HAVING AN UNSUPPORTED FIRST END AND A SUPPORTED SECOND END, FURTHER INCLUDING COUPLING MEANS CONNECTING SAID FIRST MEANS TO SAID FIRST END FOR TRANSMITTING FORCE THEREBETWEEN. AND SUPPORT MEANS FOR SAID SECOND END WHICH IS FIXED WHEN THE FORCE TRANSMITTED IN JUST BELOW THAT WHICH WOULD DAMAGE SAID SECOND MENS, AND WHICH IS RESILIENT WHEN THE FORCE IS GREATER. 